Identification of target proteins for bioactive molecules or glycoconjugates is a key issue in chemical (glyco)biology. However, capturing direct interactions between bioactive molecules and their target is still challenging, especially when the target biomolecules are low-abundance proteins and/or low-affinity binding partners. Photo-affinity labeling (PAL) has been widely accepted as one of the most powerful approaches to overcome these challenges, because covalent bond formation via photo-irradiation allows for the detection of reversible interaction, even at cell level. In this study, we report the 2-thienyl α-ketoamide as a less hydrophobic and more compact photo-reactive group, and can be used as an alternative to benzophenone for PAL.
Whereas previous reports indicated unfavorable photo-degradation for α-ketoamides, we found that the 2-thienyl group provided low electrophilicity and high photo-stability to α-ketoamides, enabling successful PAL with α-ketoamide. Using an α-ketoamide functionalized mannose and a mannose-binding protein, Concanavalin A, as a model set of interacting partners, we demonstrate the viability of 2-thienyl α-ketoamide as a photoreactive group for the capturing of low-affinity carbohydrate-protein interactions. The most characteristic feature of our new photoaffinity group is its significantly lower non-specific labeling of other proteins, compared to other representative photo-reactive groups.
- Ota, E.; Usui, K.; Oonuma, K.; Koshino, H.; Nishiyama, S.; Hirai, G.*; Sodeoka, M.*, Thienyl-Substituted alpha-Ketoamide: A Less Hydrophobic Reactive Group for Photo-Affinity Labeling. ACS Chem. Biol. 2018, 13, 876-880.